1. Field of the Invention
The present invention relates to a shield and spring interface to a spark plug from a pencil coil.
2. Discussion of the Related Art
A typical automotive ignition system includes a spark plug, for each combustion chamber of an engine, at least one ignition coil and at least one device adapted to selectively charge the coil(s) and cause the energy stored in the coil(s) to be discharged through the spark plugs in a timed manner so that a spark is generated and ignition of a fuel-air mixture in each combustion chamber occurs at a specified timing.
Recent technological advances have made it more practical and desirable to provide each combustion chamber (or cylinder) with its own dedicated coil, and to provide each coil in a relatively compact configuration at the top of each combustion chamber""s spark plug. Such coils are customarily referred to as xe2x80x9cpencil coilsxe2x80x9d. The diameters of such pencil coils enable at least a portion of the coil to extend into the spark plug well on the typical engine, thereby providing efficient use of the limited space therein.
Pencil coils typically are equipped with a conductive shield. The conductive shield surrounds the pencil coil and tends to reduce radio frequency interference (RFI) from the coil. A significant source of RFI, however, is the electrical current path from the secondary winding. In the typical pencil coil arrangement, the spark plug is grounded to the engine and the return path for the electrical current in the secondary winding to the low voltage terminal of the secondary winding is through components located outside of the shield. The secondary winding current flowing through the components located outside of the shield provides a significant source of RFI. Thus, despite the presence of the shield, the typical pencil coil arrangement does not eliminate a significant portion of the RFI caused by the secondary winding current.
There is consequently a need in the art for way of reducing the RFI caused by the secondary winding current. Since it is desirable to keep costs and complexity to a minimum, there is a need in the art for a way of reducing this RFI without significantly increasing the cost, time, or complexity of the ignition system or the manufacturing and/or installation processes associated therewith.
It is a primary object of the present invention to overcome the foregoing problems and/or to satisfy at least one of the aforementioned needs by providing a shield and spring interface to a spark plug from a pencil coil.
To achieve this and other objects and advantages, the present invention provides an interface device for interfacing a pencil coil to a spark plug. The interface device comprises a substantially C-shaped spring adapted to mechanically and electrically engage a pencil coil shield and also adapted to make electrical contact with a spark plug ground while the spring remains mechanically and electrically engaged to the pencil coil shield.
Also provided by the present invention is a pencil coil shield assembly for interfacing a pencil coil to a spark plug. The pencil coil shield assembly comprises a substantially cylindrical pencil coil and a spring. The substantially cylindrical pencil coil shield is adapted to surround the pencil coil. The spring is mechanically and electrically engaged with the pencil coil shield and is adapted to make electrical contact with a spark plug ground while the spring remains mechanically and electrically engaged to the pencil coil shield.
The present invention also provides a pencil coil shield assembly for interfacing a pencil coil to a spark plug, the assembly comprising a substantially cylindrical pencil coil shield adapted to surround the pencil coil and means mechanically engaged to the pencil coil shield, for electrically connecting the pencil coil shield with a spark plug ground.
Advantageously, the foregoing interface device and/or pencil coil shield assemblies can be configured to reduce RFI from the secondary current winding currents of a pencil coil. In addition, each can be manufactured using inexpensive and uncomplicated manufacturing and installation techniques, and using starting materials and parts that are relatively inexpensive.
Also provided by the present invention is a method of reducing RFI from secondary winding currents of a pencil coil. The method comprises the steps of providing a substantially cylindrical shield around a pencil coil, electrically connecting the substantially cylindrical shield to a low voltage terminal of a secondary winding of the pencil coil, and electrically connecting the substantially cylindrical shield to a spark plug ground of a spark plug associated with the pencil coil.
Still other objects, advantages, and features of the present invention will become more readily apparent when reference is made to the accompanying drawing and the associated description contained therewith.